The removal of particulates from working or moving fluids is vital to the prevention of the fouling or erosion of heat, mass and momentum transfer surfaces. In the particular case of electronics enclosures, contaminants in the cooling airflow may foul heat sinks and prevent proper cooling of electronic components. In the past, working and moving fluids were either sealed in a closed environment and, if necessary, cooled by the use of heat exchangers, or conventional screening filters were employed. Conventional filters require periodic maintenance, however, and heat exchangers are relatively expensive. An affordable, maintenance-free, self-cleaning filter system represents an appealing solution to the problem of particulate contamination.
Exclusion filters are a relatively new development in the field of particulate filtration. Exclusion filters utilize a cylindrical stack of evenly-spaced flat annular disks which rotates about the stack's central axis. The stack is capped on one end, and the disk's concentric holes form a central core within the stack. When operating, fluid pressure is reduced within the core and unfiltered fluid enters the rotating stack's periphery though the spaces between the disks. The fluid exits the stack through the uncapped end of the central core. Exclusion filters operate on Boundary Layer Momentum Transfer methodology. The rotation of the disks establishes a boundary layer on each side of each disk in the stack. A pressure drop across the disk stack (from outer to inner perimeter) is caused by the frictional drag losses of outside fluid traversing the boundary layers between the disks. Angular momentum transfer from the rotating disks via the inter-disk boundary layers in the device causes any particles above the critical cut-off size that are entrained in the incoming fluid to be immediately expelled away from the device perimeter. The fluid itself passes easily through the device. Exclusion filters are capable of filtering particulates and liquid droplets from a gas, or of filtering particulates from a liquid.
Prior exclusion filter systems have suffered from leakage problems. Specifically, in prior exclusion filter systems unfiltered fluid has a tendency to leak into and contaminate previously filtered fluid by way of the interface area between the rotating exclusion filter and the non-rotating bulkhead which separates the filtered fluid from the unfiltered fluid. This leakage of unfiltered fluid also contributes to the deterioration of sealing measures which may be located within the interface area, to the binding of bearings in the interface area, and to the general fouling and clogging of the interface area. Properly functioning exclusion filter systems represent an affordable, maintenance free, and self-cleaning alternative to existing filter systems, and could be used to remove particles from a moving or working fluids. A need exists for a properly functioning exclusion filter system which does not suffer from such leakage problems.